Transmission fluid formulations continue to trend to the use of lower viscosities to enhance fuel economy benefits. The benefits of moving to lower viscosity fluids is well-documented; however, the fuel economy benefits realized from a lower viscosity fluid may trade off with gear protection, wear protection, foam and aeration performance, and desired frictional characteristics. One of the requirements of a suitable low viscosity transmission fluid is an ability to pass a Ford Planetary Gear Fatigue Test. Conventional transmission fluid formulations at kinematic viscosity of less than 5 cSt at 100° C. generally cannot achieve a gear fatigue performance of greater than 40 hours. Conventional transmission fluids having kinematic viscosities of 5 cSt or greater at 100° C. may be adequate in terms of gear fatigue performance, but fail to provide suitable fuel economy benefits. The same fluid formulation at a kinematic viscosity of 4.0 cSt at 100° C. may be inadequate for gear fatigue performance. Because driveline system lubricants are moving to lower viscosities to gain overall fuel economy there is a need for lubricating fluids that provide suitable gear fatigue performance and friction performance at a kinematic viscosity below 5 cSt at 100° C.
In view of the above, embodiments of the disclosure provide a lubricant composition, a method for improving lubrication and a method for lubricating a machine. The lubricant composition includes a) a major amount of a base oil having a kinematic viscosity between 2 and 4 cSt at 100° C.; and b) dioctyl phosphite in an amount providing about 100 to about 1000 ppm phosphorus to the lubricant composition. The lubricant composition has a phosphorus weight ratio of component (b) to total phosphorus in the lubricant composition from 0.4:1 to less than about 0.8:1. In one embodiment, the base oil has a kinematic viscosity between 3 and 4 cSt at 100° C.
In one embodiment, the disclosure provides a method for improving the lubricating properties of a lubricating fluid while lubricating an automotive component. The method includes adding a lubricating fluid to an automotive component requiring lubrication, the fluid containing (a) a major amount a base oil having a kinematic viscosity at between 2 and 4 cSt at 100° C., and (b) dioctyl phosphite in an amount providing from about 100 to about 1000 ppm phosphorus to the lubricant composition. The lubricant composition has a phosphorus weight ratio of component (b) to total phosphorus in the lubricant composition of from 0.4:1 to less than about 0.8:1. The automotive component that contains the fluid is operated and exhibits an improved performance relative to the performance of a lubricating fluid free of the compound of 1) (b).
Another embodiment of the disclosure provides a lubricant composition having a kinematic viscosity of less than 5 cSt at 100° C. The lubricant composition includes (a) a major amount of base oil having a kinematic viscosity of from about 2 to about 4 cSt at 100° C., and (b) a dioctyl phosphate component in an amount providing from about 100 to about 1000 ppm phosphorus to the lubricant composition. The lubricant composition has a phosphorus weight ratio of component (b) to total phosphorus in the lubricant composition of from 0.4:1 to less than about 0.8:1 and has a gear fatigue performance of greater than 40 hours.
In one embodiment, component (b) provides from about 100 to about 750 ppm phosphorus to the lubricant composition. In another embodiment, component (b) provides from about 100 to about 600 ppm phosphorus to the lubricant composition. In yet another embodiment, component (b) provides from about 100 to about 550 ppm phosphorus to the lubricant composition, or from about 150 to about 600 ppm phosphorus to the lubricant composition.
In another embodiment a lubricant composition of the disclosure may further include an oil-soluble ashless dispersant selected from: a succinimide dispersant, a succinic ester dispersant, a succinic ester-amide dispersant, a Mannich base dispersant, and phosphorylated and/or boronated forms thereof.
In yet another embodiment of the disclosure, a lubricant composition may further include one or more of the following components selected from: an air expulsion additive, an antioxidant, a corrosion inhibitor, a foam inhibitor, a metallic detergent, an organic phosphorus compound, a seal-swell agent, and a viscosity index improver.
In still another embodiment the disclosure includes a method of lubricating a machine part comprising lubricating the machine part with a lubricant composition containing a minor amount of an additive composition as described herein.
In another embodiment, the disclosure includes a method wherein the machine part is selected from a gear, an axle, a differential, an engine, a pump, a piston, a crankshaft, a transmission, or a clutch.
In another embodiment, the disclosure includes a method wherein the transmission is selected from an automatic transmission, a manual transmission, an automated manual transmission, a semi-automatic transmission, a dual clutch transmission, a continuously variable transmission, and a toroidal transmission.
In one embodiment, the disclosure includes a method wherein the clutch is selected from a continuously slipping torque converter clutch, a slipping torque converter clutch, a lock-up torque converter clutch, a starting clutch, one or more shifting clutches, and an electronically controlled converter clutch.
In another embodiment, the disclosure includes a method wherein the gear is selected from an automotive gear, a stationary gearbox, and an axle.
In another embodiment, the disclosure includes a method wherein the gear is selected from a hypoid gear, a spur gear, a helical gear, a bevel gear, a worm gear, a rack and pinion gear, a planetary gear set, and an involute gear.
In another embodiment, the disclosure includes a method wherein the differential is selected from a straight differential, a turning differential, a limited slip differential, a clutch-type limited slip differential, and a locking differential.
In another embodiment, the disclosure includes a method wherein the engine is selected from an internal combustion engine, a rotary engine, a gas turbine engine, a four-stroke engine, and a two-stroke engine.
In one embodiment, the disclosure includes a method wherein the engine includes a piston, a bearing, a crankshaft, and/or a camshaft.
In another embodiment, the disclosure includes a method wherein the pump is selected from a positive displacement pump, a rotodynamic pump, a reciprocating pump, an impeller pump and/or a centrifugal pump.
In another embodiment, the disclosure includes a method wherein the piston is a hydraulic piston designed to extend, retract, or retract and extend, and/or resist motion.
An advantage of the compositions and methods described herein is that there is provided a lubricant fluid composition that exhibits enhanced gear fatigue properties and suitable friction performance properties in a fluid having a kinematic viscosity of less than 5 cSt at 100° C.